Entrance doorways are required on precipitators, bag houses, scrubbers and the like to allow maintenance personnel to enter through the casing of the device periodically. If, during the course of operation of the device after the entrance doorway was last opened, there has been some leakage, corrosion will occur at the juncture of the door system and casing, resulting in deterioration of the casing wall, door and door frame, as well as failure of the door gasket. This problem generally requires rather costly repair work on the door system to restore it to a proper working condition. It is the principal object of the present invention to provide an improved door system for the above-stated and similar industrial applications which will eliminate substantially the above problems arising due to opening and closing of the door system periodically.
Another important object of the invention is to provide a dual door system including an interior metal plate somewhat flexible sealing door having a high temperature acid-resistant hollow core resilient gasket around its perimeter for engagement with an opposing door frame plate on the casing wall of the industrial unit. The interior door is hinged to the door frame plate and is equipped with a means to apply pressure to the center of the interior door to flex it inwardly to a somewhat concave form, thereby assuring a tight seal. An exterior lightweight thermally insulated door panel is removably latched on the exterior end of an adjustable length sleeve extending between the interior door frame and the exterior door panel. A dead air space between the interior door and exterior insulated door panel and within the sleeve allows the temperature in the dead air space to be decreased through the acid dew point, thereby eliminating corrosion at the juncture of the interior door and the adjacent casing wall of the industrial unit.
Another object of the invention is to provide a door system of the above type for industrial devices in which the interior somewhat flexible sealing door plate is equipped with an anti-sagging means and a retracting means used to pull the interior door and its gasket away from the adjacent door frame plate when inward flexing pressure on the interior door is being released.
Other objects and advantages of the invention will become apparent to those skilled in the art during the course of the following description.